Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. In hybrid vehicles, shorter engine operation times can lead to insufficient purging of fuel vapors from the vehicle's emission control system. To address this issue, hybrid vehicles may include a fuel tank isolation valve (FTIV) between a fuel tank and a hydrocarbon canister of the emission system to limit the amount of fuel vapors absorbed in the canister. In some examples, the FTIV may be a bi-stable valve adjustable between open and closed positions via a short electrical pulse. However, a position of the FTIV during use may not be known without an additional sensor. As a result, the FTIV may be adjusted into a different position than desired during operation.
One example approach of a bi-stable isolation valve is shown by Takagi et al. in U.S. Pat. No. 6,761,154. Therein, an electromagnetically actuated open/close valve is shown in a vapor passage between a fuel tank and a fuel canister. The valve is opened and closed under different engine operating conditions; however, there may not be a way of diagnosing a position of the valve.
As one example, the issues described above may be addressed by a method for adjusting a fuel tank isolation valve (FTIV) of a fuel system by sending electrical pulses to the FTIV, counting each of the electrical pulses to track a position of the FTIV, and verifying the position of the FTIV when a vacuum is created in the fuel system. In this way, the position of the FTIV may be diagnosed, thereby resulting in increased accuracy of subsequent valve control.
For example, when a vacuum (e.g., fuel system pressure below a vacuum threshold pressure) is sensed in the fuel system, the FTIV must be closed otherwise the vacuum may not be achieved. Thus, verifying the position of the FTIV may include verifying the FTIV is closed when a vacuum is sensed in the fuel system. Additionally or alternatively, the FTIV may be verified as closed responsive to a fuel tank pressure greater than a threshold pressure. A vacuum may be applied to the fuel system in response to the position of the FTIV being unknown, a duration since last diagnosing the FTIV position, and/or a request to run a leak check routine in the fuel system. In one example, a controller may operate a vacuum pump of an evaporative leak check module (ELCM) in order to apply the vacuum to the fuel system. If no vacuum is sensed after applying the vacuum to the fuel system, the controller may determine the FTIV is open.
After diagnosing the position of the FTIV, the controller may adjust the FTIV into a desired position. In one example, adjusting the FTIV to the desired position includes sending an electrical pulse to actuate the FTIV from a first position to the desired position. In another example, adjusting the FTIV to the desired position may include not sending the electrical pulse to actuate the FTIV when the FTIV is already in the desired position. In some examples, degradation of the FTIV may also be determined if the FTIV is verified as being open when it is supposed to be closed. Thus, as a result of applying a vacuum to the fuel system, the position of the FTIV may be determined and used for subsequent valve control.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.